1. Field of the Invention
The present invention relates generally to communication systems, and more specifically to transmitting information among multiple physical upstream channels in a communication system.
2. Related Art
Communication systems include nodes that are coupled to each other via channels. A channel need not necessarily have a physical structure. For instance, in many communication systems, a channel is defined by a carrier signal having a predetermined frequency. Communication systems often include at least one supervisory node and a plurality of remote nodes. Communications from a supervisory node to a remote node are referred to as downstream communications and are transferred via downstream channel(s). Communications from a remote node to a supervisory node are referred to as upstream communications and are transferred via upstream channel(s).
Additive white Gaussian noise (AWGN) is often used to simulate or approximate the noise that is associated with a channel. According to communications theory, channels operating in noise, such as AWGN, have theoretical capacity limits. For example, the maximum data rate (RMAX) associated with a channel is limited by the average transmit power (PAVE), the signal-to-noise ratio (SNR), the bandwidth for the channel, and the upstream modulation technique. For a signal that is modulated using digital symbols, the average transmit power and the modulation technique determine the maximum number of bits that may be transmitted per symbol. The SNR determines the minimum average transmit power that is necessary to distinguish the signal from the AWGN. The bandwidth determines the maximum number of symbols that may be transmitted per second. The maximum data rate of a channel may be represented as RMAX=X*Y, where X is the maximum number of bits that may be transmitted per symbol via the channel, and Y is the maximum number of symbols that may be transmitted per second via the channel.
In general, increasing the average transmit power by 3 dB enables an additional bit of information per symbol to be transmitted for a given SNR, bandwidth, and modulation technique, thereby increasing the maximum data rate of the channel. However, increasing the average transmit power may not be desirable due to any of a variety of reasons, including but not limited to a) increased cost, b) lower reliability, c) increased noise in adjacent and/or other channels, d) battery lifetime, and e) power limitations of the communication system.
Accordingly, systems and methods are needed that address one or more of the aforementioned shortcomings of conventional communication systems and methods.
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